Method of separation



United 2,849,282 Patented Aug. 26, W58

2,849,282 METHOD OF SEPARATION George E. Boyd, Oak Ridge, Tenn., assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application August 14, 1944 Serial No. 549,477

9 Claims. (c1. 23-145 and advantages description.

In the following description, the isotope of element 93 having a mass of 239 is referred to as 93 and the isotope of element 94 having a mass of 239 is referred to as 94 Element 94 may also be designated as plutonium, symbol Pu. Reference herein to any of the understood as denoting the element generically, whether in its free state or in the form of a compound, unless indicated otherwise by the context.

Neutron irradiated uranium may be prepared by reacting uranium with neutrons from any suitable neutron source.

' Neutron irradiation of uranium produces U which has a half-life of 23 minutes and by beta decay becomes 93. This element has a half-life of 2.3 days and by beta decay becomes 94 Neutron irradiated uranium contains 93 94 and a large number of radioactive fission products produced by reaction of neutrons on fissionable atoms, such as U which is present in uranium from natural sources. It also contains minor amounts of other products such as UX and UX Inasmuch as the 93 and 94 content of neutron irradiated proximately .02 percent by weight of the irradiated uranium. By storing the neutron irradiated uranium for a suitable period of time, the 93 is converted almost entirely to 94 Thefission products are present in the neutron irradiated uranium generally to an extent of about 0.02 percent by Weight. Because the fission products in general are highly radioactive, it is desirable that these materials be removed.

The fission products consist of a large number of elements which may be classified into two groups; a light group with atomic numbers from 35 to 45; and a heavy group with atomic numbers from 51 to 60. The fission products with which we are particularly concerned are those having a half-life of more than three days since they remain in the neutron irradiated reaction mass in sub stantial quantities at least one month after reaction. The products are chiefly radioactive isotopes of Sr, Y, Zr, Cb, and Ru of the group of atomic numbers from 35 to 45; and Te, I, Xe, Cs, Ba, La, and Ce from the group of atomic numbers from 51 to 60, inclusive.

In accordance with this invention, a solution of the neutron irradiated uranium is flowed through an adsorbent. .Where two or more substances having different strengths of attraction for the adsorbent are treated, there will be a tendency for the substances to be adsorbed in strata or layers. Generally speaking, the order of adsorption and position of the adsorbed substance in a column of adsorbent is dependent upon the adsorptionaflinity of the particular adsorbate; the layers of adsorbates having higher adsorption aflinities will, in the case of downward flow of solution through the adsorbent, be above the layers of those having lower adsorption-afiinities. This type of adsorption is known aschromatographic adsorption and, because of the nature and concentration of the substances present in neutron irradiated uranium, is especially suitable for the separation of such substances from each other, particularly the separation of plutonium from the uranium and certain of the fission products.

The plutonium, when referred to in the following description, is in its reduced or phosphate insoluble state (in a valent state of 3 or 4 but not above 4).

If the original solution is passed for a considerable length of time through the adsorbent, the various strata of adsorbed material become progressively lowered in the case of downward flow of solution in the column. Thus, the column originally having layers of adsorbed plutonium, fission products, and uranium, will soon consist substantially of layers of plutonium and fission products, and finally will contain only a single layer of plutonium. It is contemplated that advantages will result from carrying the process to any one of these three stages in obtaining the desired separation or removal of any one of the three substances mentioned, and consequently all such modifications are considered to come within the scope of my invention.

Where the chromatographic process is carried to the first stage so that the plutonium is concentrated in the upper layer, the fission products in a middle layer, and the uranium in a lower layer, the individual layers may be treated by one of several methods to remove the particular substance to be eliminated. Also, the column may be constructed to permit division into chambers after the layers are formed so that one or more layers may be treated separately within the column to remove the particular adsorbed substance or substances.

Preferably, the adsorbates are removed by flowing wash solutions through the adsorbent, thereby causing the substance having the' lowest adsorption-aflinity to gradually move down the column by a continuous process of desorption and adsorption resulting from the uni-directional permeation of the wash solution. Eventually, the adsorbate passses out of the column with the wash solution and is collected as a separate fraction. layer of adsorbate having the next highest adsorptionaflinity will have moved down the column and will pass out of the column upon continued washing, where it is collected as a separate fraction. The washing is continued until all the substances to be separated have passed out of the column. Where plutonium, fission products,

the column, will go out next and the plutonium layer last. As the fission products usually comprise several elements, each having a slightly different adsorption-afiinity, the

fission products layer may overlap the plutonium and uranium layers somewhat and prevent a compl te separation.

While it is contemplated that such chromatographic adsorption for the separation of substances present in a solution of neutronirradiated i anium may be carried out with any adsorbent, including both inorganic adsorbents such as silica gel, alumina, diatornaceous earth, and the like, and organic adsorbents such as activated ca bon, sulphonated carbonaceous material Z eo-ca 3b, phenol; formaldehyde resins, preferably those containing .sulphonic acid groups either as such orhaving their hydrogen atoms replaced by cations which are exchangeable for the cations in the solution undergoing adsorption, and the lil e, particularly advantageous results are obtained by the use of ion exchange adsorbents in which the cation of the adsorbent is exchanged for a similarly charged ion of the substance to be adsorbed. It has been found that the process is particularly effective where the adsorbent used is a relatively inert, organic material containing sulphonic acid groups. Thus, the adsorbent may comprise phenol-formaldehyde resins, phenol-tannic acid resins, lignite products, or the like, which contain numer: ous RSO R" groups in which R is an organic group and in which R is hydrogen or a replaceable cation, although R is preferably H+ or Na Preferably, the adsorbent is a phenol-formaldehyde condensation product containing such sulphonic acid groups. In the adsorption process, the hydrogen or other cation of the sulphonic acid group is replaced by a cation ofthe substanceto be adsorbed which thereupon forms a more or less loosely associated molecule with the residue. i

As an example of a method by which a sulphonated resin may be prepared, 175 parts of 1-hydroxybenzene1 4-sulphonic acid are heated together with 40 parts of a formaldehyde solution of 30 percent strength for one: half hour to about 105 C. Then, further 60 parts of formaldehyde are'added and the temperature is kept for about ten hours at9 C. A hard black resin is formed.

which is stable to water and of conchoidal fracture. This resin is washed with water and ground to a powder.

By regeneration with an acid or a solution of common.

salt, this base-exchanging body regains its original ab.- sorptlon-capacity.

The overall rate of adsorption of the plutonium, urani-,,

um, and fission products "is, "generally dependent upon the. particle size of theadso rbent-in that more finely divided adsorbents will give an increased adsorption where the plutonium is in contact with the adsorbent for only a short period of time. Thus, a sulphonated phenol-formaldehyde resin of average particle size of 30 mesh will glve only 75 percent. adsorption as compared to the adsorption of 100-200 mesh resin, where in both instances the plutonium is in contact with the adsorbent for ten minutes. Where the time of contact'is two hours or more, the difference betweenarnounts adsorbed is negligible. In carrymg out the process, the adsorbent is held In an elongated container commonly referred to as a column. To facilitate the formation of layers or strata of adsorbed substances, the column is preferably of relatively small diameter, or cross-section in proportion to its length. The bottom of the column is constructed to permit the passage of the solutionstherethrough While retaining the adsorbent thereon. Tightly 'woven metal screens, glass wool, and the like may be employed for this purpose. The adsorbent is loosely packed in the column with its bed depth adjusted to the number and amounts of adsorbates in the solution to be treated. The. particle size of the adsorbent is important in that the smaller the particle size, the more rapid the overall rate of adsorption, although the adsorbentmust not be so fine as to greatly impede the rate of flow of the solutions through the column. Where ion-exchange resins. of the, sulphonated phenol-formaldehyde type are used, aparticle size of between 60-100 mesh has been found to be satisfactory.

After the column has been prepared, the solution containing the substances to be adsorbed is flowed through the adsorbent. For the layers of strata of adsorbates to be formed, the solution must percolate or flow through the column in one direction. As the solution flows through the adsorbent, layers of the components are formed in the column according to their adsorption aflinities. Where several of the components have similar adsorption-allianties, the layers of these adsorbates may overlap.

The wash solution or solutions used to desorb the adsorbed substances from the adsorbent may be any solution containing cations exchangeable for "the. ions to be desorbed. It will be understood that the wash solution will be effective to remove adsorbate from the adsorbent until such time as substantial equilibrium is reached between the ratio of desorption and readsorption of the particular cation or cations being desorbed. While the dissolved ,adsorbate may be readsorbed along the column, further amounts of wash solution will again desorb the substances; this will continue until the adsorbate passes out of the column. Water may provide a sufficient condition of dilution for desorption, although excessive amounts may be required. In the case of plutonium, fission products, and uranium, it has been found that aqueous solutions, of acids are particularly suitable because of the speed of desorption and the relatively small amounts of wash solution required, probablydue to their high degree of dissociation. Aqueous solutions of mineral acids such as H 50 HCl, or HNO and acid salts such as NaHSO in varying concentrations, have been used satisfactorily.

In accordance with one embodiment of the invention, the neutron irradiated uranium containing, for example, approximately 0.01 percent by weight, of plutonium and a similar concentration of fission products is dissolved in nitric acid to form uranyl nitrate. UO (NO The uranyl nitrate is made up in a 10 percent solution based on uranyl nitrate hexahydrate, which is adjusted to a pH value between 1 and 3.

i The uranyl nitrate hexahydrate solution containing the Pu in solution isthen passed through a column containing a catiomexchange, sulphonated phenol-formaldehyde resin of 60-100 mesh particle size. The amountof adsorbent used is preferably proportional to the quantity of 10 percent uranyl nitrate hexahydrate solution to be run through the column. To separate plutonium, fission products, and uranium, it is desirable to have at least approximately 0.15 pound of the sulphonated phenol-formaldehyde resin for each. pound of neutron irradiated uranyl nitrate hexahydrate in the solution to be treated; the preferred proportionis approximately 0.19 pound of the sulphonated phenol-formaldehyde resin for each pound of the neutron irradiated uranyl nitrate hexahydrate in the solution.

The rate of flow of the uranyl nitrate. hexahydrate solution through the column is approximately 0.632 gallon per hour where the column is 2.7 inches in diameter (bed area approximately 0.04 square foot) and 5.1 inches in length. The 3.79 gallons-of 10 percent uranyl nitrate hexahydrate solu'tionis passed through the column containing 0.66 pound of'adsorbcnt in approximately six hours, the ratio of adsorbent in this instance being approximately 0.22 pound of sulphonated phenol-formaldehyde resin for each pound of neutron irradiated uranyl nitrate activity, 16 percent of the gamma activity, and 2.5 percent of the plutonium. The amounts of plutonium, uranium, and fission products in this fraction and in the fractions to be later described are given as percentages of the total amounts present in the original neutron irradiated uranium nitrate hexahydrate solution prior to adsorption. The amount of fission products in a given fraction is expressed in terms of the total beta activity and the total gamma activity resulting from the presence therein of one or more fission products.

A desorbing solution, as, for example, a solution be tween 0.2 M and 0.3 'M in H 80 was flowed through the column to remove substantially all of the adsorbed uranium, this wash solution being collected as a separate fraction. The volume of such wash solution may be, for example, between 17 percent and 21 percent of the volume of the original uranyl nitrate hexahydrate solution flowed through the column. This wash solution, containing the desorbed uranium together with minor amounts of desorbed plutonium and desorbed fission products, was found to contain, of the amount of substances originally present, approximately 13 percent of the uranium, 3.6 percent of the beta activity, and 0.5 percent of the plutonium. The fraction obtained by collecting this first wash solution together with the fraction obtained by collecting the original neutron irradiated uranyl nitrate hexahydrate solution after it had passed through the column, contained substantially all of the uranium as well as moderate amounts of fission products and minor amounts of plutoni To remove as much of the fission products as possible, a second wash solution, as, for example, a solution being approximately 0.6 M in H PO and 1 M in HNO was passed through the column. The volume of this wash solution maybe, for example, approximately 15 percent of the volume of the original uranyl nitrate hexahydrate solution flowed through the column. This wash solution desorbed substantial amounts of fission products and when collected as a separate fraction was found to contain of the amount of substances originally present approximately 25 percent of the beta activity, 42 percent of the gamma activity, and 5 percent of the plutonium.

A third wash solution, as, for example, a solution being approximately 0.8 M in H PO and 1 M in HNO was passed through the column to desorb the plutonium. The volume of this wash solution may be, for example, approximately percent of the volume of the original uranyl nitrate hexahydrate solution flowed through the column. After passing through the column, this wash solution was found to contain of the substances originally present approximately 28 percent of the beta activity, 32 percent of the gamma activity, and 92 percent of the plutonium.

Certain of the fission products have adsorption-afiinities sufficiently close to those of plutonium and uranium that the latter fractions may contain moderate amounts of fission products. If desired, these fractions may be further purified.

The above detailed description has been given for purposes of illustration and the invention is to be limited only by the scope of the following claims.

I claim:

1. A method of separating values of uranium, plutonium, and fission products which comprises flowing a solution containing uranium ions, fission product ions, and plutonium ions through a column containing a cation exchange resin whereby the ions of uranium, fission products, and plutonium are adsorbed, desorbing said adsorbed uranium ions with a solution of between 0.2 M and 0.3 M in H 80 desorbing said adsorbed fission product ions with a solution approximately 0.6 M in H PO and approximately 1 M in HNO and desorbing said adsorbed plutonium ions with a solution of approximately 0.8 M in H PO and approximately 1 M in H-NO 2. A method of separating values of uranium, plutoadsorbent cation exchange 6 nium, and fission products which comprises flowing a solution containing uranium ions, fission product ions, and plutonium ions through a column containing a phenol formaldehyde cation exchange resin having sulphonated acid groups associated therewith whereby the ions of uranium, fission products, and plutonium are adsorbed, desorbing said adsorbed uranium ions with a solution between 0.2 M and 0.3 M in H desorbing said adsorbed fission product ions with a solution approximately 0.6 M

in 'H PO and approximately 1 M in HNO and desorbing said adsorbed plutonium ions with a solution approximately 0.8 M in H PO and approximately 1 M in HNO 3. A method of separating plutonium ions from uranium ions in an aqueous solution containing ions of uranyl uranium and ions of plutonium in a valence state not above 4 which comprises contacting the solution with an resin in amount sufficient toadsorb plutonium ions but insufiicient to adsorb all of the uranium ions and separating the solution containing unadsorbed uranium ions from the adsorbent cation exchange resin containing plutonium.

4. A method of separating plutonium ions from uranium ions in aqueous solution containing ions of uranyl uranium and plutonium in a valence state not above 4 which comprises contacting a portion of the solution with an adsorbent cation exchanger resin to adsorb ions of plutonium and uranium and contacting the exchanger with further portions of the solution to increase the concentration of plutonium ions by replacement of uranium ions in the adsorbent cation exchange resin.

5. A method of separating plutonium ions and uranium ions in an aqueous solution containing ions of uranyl uranium and plutonium in a valence state not above 4 which comprises passing the solution through a porous bed of an adsorbent cation exchange resin to adsorb plutonium ions and continuing passage of solution through the bed until the ratio of plutonium values to uranium values in a portion of the bed is substantially higher than the initial ratio of plutonium ions to uranium ions in the solution.

6. A method of separating plutonium ions from uranium ions in an aqueous solution containing a major amount of uranyl ions and a minor amount of ions of plutonium in a valence state not above 4 which comprises contacting the solution with a sulfonated phenyl-formaldehyde cation exchange resin in amount sufiicient to adsorb plutonium ions but insufiicient to adsorb all of the uranium ions and separating the solution containing unadsorbed uranium ions from the resin containing plutonium values.

7. A method of separating plutonium ions from uranium ions contained in an aqueous solution containing ions of uranium and plutonium which comprises contacting a portion of the solution with a sulfonated phenyl-formaldehyde cation exchange resin to adsorb ions of plutonium and uranium and contacting the resin with further portions of the solution to increase the concentration of plutonium values by replacement of uranium values in the resin.

8. A method of separating ions of fission products from ions of uranium in a solution thereof which comprises con tacting the solution with an adsorbent cation exchange resin in amount sufiicient to adsorb fissionproduct ions:

insufiicient to adsorb all of the uranium ions,

removing the solution containing unadsorbed uranium ions; and eluting adsorbed compounds of said material from the;

exchanger with an acid solution.

(References on following page) separating a material consisting of uranyl uranium and ions of said material with a sulfonated phenyl-formaldehyde cation ex-- change resin 1n amount sufiicient to adsorb ions of said References Cited in the file of this patent ErdenoneyeretaL: Chem. Abstracts, vol. 36, page 2221 UNITED STATES PATENTS 1- I 1,120,551 Schwerln Dec. 8, 1914 333 a1 Chem Abstracs vol 3 Page 319 2,184,943 Pattock Dec. 26, 1939 5 2,204,072- Dean, June 11 19-40 2 m- Abstracts, 37, p 6517 2,204,539 Waseneger June 11, 1940 2,275,210 Urbain 'Mar; 3, 1942 OTHER REFERENCES Myers et 2112 Chem. Abstracts, Vol. 35, page 4870 (1941). 

1. A METHOD OF SEPARATING VALUES OF URANIUM, PLUTONIUM, AND FISSION PRODUCTS WHICH COMPRISES FLOWING A SOLUTION CONTAINING URANIUM IONS, FISSION PRODUCT IONS, AND PLUTONIUM IONS THROUGH A COLUMN CONTAINING A CATION EXCHANGE RESIN WHEREBY THE IONS OF URANIUM, FISSION PRODUCTS, AND PLUTONIUM ARE ABSORBED, DESORBING SAID ADSORBED URANIUM IONS WITH A SOLUTION OF BETWEEN 0.2 M AND 0.3 M IN H2SO4, DESORBING SAID ADSORBED FISSION PRODUCT IONS WITH A SOLUTION APPROXIMATELY 0.6 M IN H3PO4 AND APPROXIMATELY 1 M IN HNO3, AND DESORBING SAID ADSORBED PLUTONIUM IONS WITH A SOLUTION OF APPROXIMATELY 0.8 M IN H3PO4 AND APPROXIMATELY 1 M IN HNO3. 